Deutsche Bank is among lenders to whom Jared has given personal guarantee. In 2015, convicted felon George Soros became an investor in Jared’s company including a $250 million line of credit. Trump declared his candidacy on June 16, 2015-Wall St. Journal, May 3, 2017

The previously undisclosed business relationships with titans of the financial and technology worlds are through a real-estate tech startup called Cadre that Mr. Kushner cofounded and currently partly owns.

In his disclosure form filed earlier this year [2017], Mr. Kushner didn’t identify Cadre as among his hundreds of assets. The Journal identified his Cadre stake through a review of securities and other filings as well as interviews with people familiar with the company and Mr. Kushner’s finances.

Jamie Gorelick, a lawyer representing Mr. Kushner, said in a statement that his stake in Cadre is housed in a company he owns, BFPS Ventures LLC. His ownership of BFPS is reported on his disclosure form, although it doesn’t mention Cadre.

Ms. Gorelick said the Cadre stake is described in a revised version of his disclosure form that will be made public after it has been certified by ethics officials. She said Mr. Kushner has previously discussed his Cadre ownership with the Office of Government Ethics and that Mr. Kushner has “resigned from Cadre’s board, assigned his voting rights and reduced his ownership share.”

A spokesman for the Office of Government Ethics didn’t respond to a request to comment.

Ms. Gorelick said it is “very normal” for a financial-disclosure form to be revised and that the form was prepared by Mr. Kushner’s lawyers on his behalf. A White House spokeswoman referred questions to Mr. Kushner’s lawyer.

Trevor Potter, a Republican former chairman of the Federal Election Commission, and other ethics experts said investments such as Mr. Kushner’s ownership of Cadre typically need to be disclosed. They said Mr. Kushner didn’t appear to violate disclosure rules by not publicly reporting his business-related debts and guarantees. But they said such arrangements ideally should be disclosed, in part because they could force Mr. Kushner to recuse himself from certain issues involving the lenders.

“Anything that presents a potential for the conflict of interest should be disclosed so that the public and the press can monitor this,” Mr. Potter said.

Ethics experts’ concern is that Mr. Kushner’s business connections could jeopardize his impartiality in certain areas and that, absent disclosures, the public is in the dark about potential conflicts.

Mr. Kushner’s rapidly expanding responsibilities range from working on a Middle East peace deal to making the federal government operate more efficiently. As a senior federal official, he is bound by ethics laws that require him to recuse himself from matters that would directly affect his financial interests.

Ms. Gorelick, who was deputy attorney general in former President Bill Clinton’s administration, said Mr. Kushner will “recuse consistent with government ethics rules.”

Mr. Kushner, the 36-year-old scion of a real-estate family, agreed with federal ethics officials to divest himself of more than 80 assets after he and his wife, Ivanka Trump, were hired by her father, President Donald Trump, as senior aides. White House officials have said some of the sales were needed to avoid potential conflicts between Mr. Kushner’s far-reaching job duties and his personal financial interests.

To get off the ground,Cadre turned to a Goldman Sachs fundand a number of high-profile investors. Among them were the venture-capital firms of Mr. Thiel, Silicon Valley’s most prominent supporter of the GOP president, and Vinod Khosla, a co-founder of Sun Microsystems Inc., according to Cadre’s website. Personal backers include Chinese entrepreneur David Yu, co-founder with Alibaba Group Holding Ltd.’s Jack Ma of a Shanghai-based private-equity firm, hedge-fund manager Daniel Och and real-estate magnate Barry Sternlicht, people close to Cadre said.

Cadre has solicited money from investors for several Kushner Cos. real-estate projects, according to information sent to prospective investors and reviewed by the Journal. Jared Kushner personally has stakes in some of the real-estate projects for which Cadre has raised money, according to Cadre documents and his disclosure form.

Mr. Williams, chief executive of Cadre, said the company has been working with regulators to update its public filings to “reflect Jared’s nonoperational, nonmanagement relationship with the company, which has been in place since the inauguration.”

BFPS Ventures, the company that Mr. Kushner’s lawyer said holds his Cadre stake, is shown on his financial-disclosure form as owning unspecified New York real estate valued at more than $50 million. The form adds that “the conflicting assets of this interest have been divested.”

Beyond Cadre, some of the assets Mr. Kushner is holding on to are hard to pinpoint, partly because they are housed in entities with generic names such as “KC Dumbo Office,”according to the disclosure form.

The Journal matched many of the assets to specific real-estate investments. An analysis of the debts on those properties, using real-estate data services PropertyShark and Trepp LLC as well as property records, found ties to a broad swath of U.S. and foreign banks, private-equity firms, real-estate companies and government-owned lenders.